The present invention relates to a cylinder throw-on/off apparatus and cylinder throw-on/off method for a printing press, in which throwing-on/off operation (impression throw-on/off) of a blanket cylinder with respect to a plate cylinder or impression cylinder is performed in a printing press such as an offset rotary printing press.
Conventionally, as a cylinder throw-on/off apparatus of this type, one disclosed in Japanese Patent Laid-Open No. 7-299897 (reference 1) is available. In the cylinder throw-on/off apparatus described in reference 1, an electric motor (stepping motor) is used as a drive source to pivot an eccentric bearing, and a blanket cylinder axially supported by the eccentric bearing is thrown on/off with respect to a plate cylinder and impression cylinder.
FIG. 13 is a side view of the main part of an offset rotary printing press described in reference 1. As shown in FIG. 14, the offset rotary printing press comprises a plate cylinder 1, blanket cylinder 2, and impression cylinder 3 for each printing unit 10. A printing plate (plate) is mounted on the plate cylinder 1. During printing, the blanket cylinder 2 is in contact with the plate cylinder 1. A blanket is mounted on the outer surface of the blanket cylinder 2. During printing, the blanket cylinder 2 is brought into contact with the impression cylinder 3 through a printing target sheet (not shown). The plate cylinder 1, blanket cylinder 2, and impression cylinder 3 constitute a printing section 31.
In such a conventional offset rotary printing press, a stepping motor serving as a cylinder throw-on/off motor 6 is fixed to a stud 5, close to the end shaft of the impression cylinder 3 and projecting outward from one frame 4, such that a drive rod 7 extends upright. When the cylinder throw-on/off motor 6 rotates, the drive rod 7 moves forward/backward vertically to pivot an eccentric bearing 8, so that throwing-on/off operation (impression throw-on/off) of the blanket cylinder 2 with respect to the plate cylinder 1 and impression cylinder 3 is performed.
During impression throw-on, the throw-on operation of the plate cylinder 1 for the blanket cylinder 2 takes place within a range excluding the printing ranges of the two cylinders, i.e., within the range of an angle θ1 shown in FIG. 15A, where notches P and B, indicated by reference symbols BC and PC, which are the notches (portions where a plate clamp, blanket fixing device, and the like are provided) of the plate cylinder 1 and blanket cylinder 2, respectively, are in contact with each other, so the film thickness of the ink applied to the plate will not be adversely affected.
Similarly, during impression throw-on, the throw-on operation of the blanket cylinder 2 for the impression cylinder 3 takes place within a range excluding the printing ranges of the two cylinders, i.e., within the range of an angle θ2 shown in FIG. 15B, where notches B and I, indicated by reference symbols BC and IC, which are the notches (portions where a blanket fixing device, a mechanism which holds a printing target sheet, and the like are provided) of the blanket cylinder 2 and impression cylinder 3, respectively, are in contact with each other, so the film thickness of the ink transferred onto the blanket on the blanket cylinder 2 will not be adversely affected and that the outer surface of the impression cylinder 3 will not be contaminated with the ink.
After impression throw-on takes place in this manner, when sheet feed is started, the image transferred from the plate on the plate cylinder 1 onto the blanket on the blanket cylinder 2 is transferred to a sheet 9 passing between the blanket cylinder 2 and impression cylinder 3, thus performing printing. When the printing operation is finished, the throw-off operation of the blanket cylinder 2 from the impression cylinder 3 takes place at the impression throw-on timing described above, i.e., within the range of the angle θ2 where the notches B and I are in contact with each other, and the throw-off operation of the blanket cylinder 2 from the plate cylinder 1 takes place at the impression throw-on timing described above, i.e., within the range of the angle θ1 where the notches P and B are in contact with each other.
According to reference 1, the speeds of the printing press during impression throw-on and impression throw-off are determined to be constant. The throw-on/off operation of the blanket cylinder 2 with respect to the plate cylinder 1 and impression cylinder 3 is performed in accordance with the predetermined operation patterns (a curve representing the relationship between the rotation phase of the printing press and the drive amount of the cylinder throw-on/off motor) of the cylinder throw-on/off motor.
[Impression Throw-on (Throw-on Operation)]
In order to suppress the influence of the impact caused by impression throw-on, the slower motion speed is determined as the speed of the printing press during impression throw-on, and sheet feed is performed by setting the speed of the printing press at a constant slower motion speed. When the rotation phase of the printing press reaches an impression throw-on start phase, the operation pattern of the cylinder throw-on/off motor is loaded, and the throw-on operation (impression throw-on) of the blanket cylinder 2 for the plate cylinder 1 and impression cylinder 3 is performed. This impression throw-on is performed sequentially by starting from the upstream printing unit 10 (10-1). When impression throw-on of the last printing unit (10-4) is completed, the speed of the printing press is accelerated to the printing speed.
[Impression Throw-Off (Throw-Off Operation)]
In order to suppress the influence of the impact caused by impression throw-off, the slower motion speed is determined as the speed of the printing press during impression throw-off. When stopping the printing press, the printing press is decelerated from the printing speed to the slower motion speed. At a constant slower motion speed, when the rotation phase of the printing press reaches an impression throw-off start phase, the operation pattern of the cylinder throw-on/off motor is loaded, and the throw-off operation (impression throw-off) of the blanket cylinder 2 from the plate cylinder 1 and impression cylinder 3 is performed. This impression throw-off is performed sequentially by starting from the upstream printing unit 10 (10-1). When impression throw-off of the last printing unit (10-4) is completed, the printing press is stopped.
With the conventional cylinder throw-on/off apparatus described above, impression throw-on/off is performed after setting the speed of the printing press at, e.g., a constant slower motion speed. It takes time until printing at the printing speed is actually started. It also takes time until the printing press is stopped. This degrades the operation rate of the printing press. The degradation of the operation rate, i.e., the time loss, increases as the number of printing units increases.
In the conventional cylinder throw-on/off apparatus described above, the predetermined operation pattern of the cylinder throw-on/off motor is indicated by a curve representing the relationship between the rotation phase of the printing press and the drive amount of the cylinder throw-on/off motor. The throw-on/off operation of the blanket cylinder 2 with respect to the plate cylinder 1 and impression cylinder 3 is performed in accordance with the operation pattern of the cylinder throw-on/off motor. In this case, considering the fact that the speeds of the printing press during impression throw-on and impression throw-off are set constant, the impression throw-on/off operation of the blanket cylinder 2 with respect to the plate cylinder 1 and impression cylinder 3 would be performed only by plotting the axis of rotation phase of the printing press in the operation pattern of the cylinder throw-on/off motor along the time axis and reading the drive amount of the cylinder throw-on/off motor at every predetermined time interval.